Exhaust manifold

ABSTRACT

An exhaust manifold ( 4 ), which is joined to a catalyst container ( 3 ) for accommodating a catalyst ( 2 ) with a tilt angle, includes: a plurality of branch pipes ( 6   a   , 6   b,    6   c,    6   d ) communicating with corresponding discharge ports (E 1,  E 2,  E 3,  E 4 ) of an engine; an exhaust collecting portion ( 7 ) where the plurality of branch pipes are collected; and a partition plate ( 8 ) dividing the interior of the exhaust collecting portion ( 7 ). The partition plate ( 8 ) is cut away to provide a cut ( 9 ) at an end surface portion ( 8 A) located toward the catalyst ( 2 ).

TECHNICAL FIELD

The present invention relates to a catalyst integrated exhaust manifold,and particularly to a structure of an exhaust manifold which is joinedto a catalyst container with a tilt angle.

BACKGROUND ART

Various proposals have been made for catalyst integrated exhaustmanifolds for the purposes of preventing interference of exhaust gasdischarged from each discharge port of the engine to improve the engineoutput as well as efficiently cleaning exhaust gas.

For example, Japanese Laid-open Patent Application No. 2001-164937(paragraphs [0014] to [0019] and FIGS. 1-7) discloses a catalystintegrated exhaust manifold including a plurality of branch pipescommunicating with corresponding discharge ports of an engine, anexhaust collecting portion where the plurality of branch pipes arejoined integrally, a catalyst container joined to the exhaust collectingportion, and a catalyst accommodated in the catalyst container, whereina partition wall is provided within the exhaust collecting portion sothat the interior of the exhaust collecting portion is divided into twochambers, and the branch pipes respectively joined to the dischargeports of the cylinders that are not continuous in the order of exhaustprocesses are collected and communicated with each chamber.

Japanese Laid-open Patent Application No. 2000-110555 (paragraphs [0007]to [0011] and FIGS. 1-4) discloses a catalyst integrated exhaustmanifold having a clearance between an exhaust downstream end edge ofthe partition wall, which divides the interior of the exhaust collectingportion into two chambers, and the catalyst such that a clearance areabecomes not more than a predetermined rate of the exhaust passagecross-sectional area positioned at the exhaust downstream end edge ofthe partition wall to prevent interference of exhaust gas.

These catalyst integrated exhaust manifolds are intended for use in thetype where the exhaust collecting portion is linearly joined to thecatalyst container.

However, the exhaust collecting portion is often joined to the catalystcontainer with a tilt angle because of a problem such as engine layout.

In a catalyst integrated exhaust manifold 101 as illustrated in FIG. 6,an exhaust manifold 104 is jointed to a catalyst container 103 foraccommodating a catalyst 102 with a tilt angle. The exhaust manifold 104consists of a plurality of branch pipes 106 each joined to correspondingdischarge ports of the engine via a discharge port flange 105, anexhaust collecting portion 107 where the plurality of branch pipes 106are collected, and a partition plate 108 for dividing the interior ofthe exhaust collecting portion 107.

This kind of catalyst integrated exhaust manifold 101 has drawbacks suchas deterioration of the catalyst 102 and disturbance of smooth exhaustgas discharge because exhaust gas flows in a biased manner with respectto the catalyst 102 and always hits the catalyst 102 in certain areas ofa plurality of gas flow passages 102 a.

Further, this kind of catalyst integrated exhaust manifold 101 has adrawback in that each of the chambers divided by the partition plate 108is provided with an O₂ sensor, thereby resulting increased manufacturingcost.

In view of the above, the present invention seeks to provide a catalystintegrated exhaust manifold of the type where an exhaust manifold isjoined to a catalyst container with a tilt angle, and which can preventboth deterioration of the catalyst and retention of exhaust gas due tobiased flow of exhaust gas.

The present invention also seeks to provide a catalyst integratedexhaust manifold which can decrease the manufacturing cost.

DISCLOSURE OF THE INVENTION

In a catalyst integrated exhaust manifold including an exhaustcollecting portion divided by a partition plate, exhaust gas flowsintermittently into the exhaust collecting portion so that a pressuredifference causes between the chamber into which exhaust gas has beenflowing and the opposite chamber into which exhaust gas has not beenflowing. We therefore propose to disperse a flow of gas by using exhaustgas flowing from one chamber to the other due to a pressure differencecaused between the chambers and to prevent a large amount of gas fromflowing into a catalyst at one time.

According to one aspect of the present invention, an exhaust manifoldwhich is joined to a catalyst container for accommodating a catalystwith a tilt angle, includes: a plurality of branch pipes communicatingwith corresponding discharge ports of an engine; an exhaust collectingportion where the plurality of branch pipes are collected; and apartition plate dividing an interior of the exhaust collecting portion,wherein the partition plate is cut away at an end surface portionlocated toward the catalyst.

According to this exhaust manifold, providing a cut at the end surfaceportion of the partition wall that is located toward the catalyst allowspart of exhaust gas that has flowed into each chamber divided by thepartition plate to flow into the opposite chamber through the cut andthereafter to flow toward the catalyst. This can alleviate aconcentration of the flow of exhaust gas at a certain region of thecatalyst and prevent deterioration of the catalyst and retention ofexhaust gas due to biased flow of exhaust gas.

According to the present invention, the aforementioned exhaust manifoldmay be provided with a sensor at the cut-away portion of the partitionplate.

According to this exhaust manifold, because a sensor such as an O₂sensor is positioned in the cut-away portion of the partition plate, itis not necessary to provide a sensor for each chamber thereby decreasingthe manufacturing cost. Exhaust gas flowing to the opposite chamberthrough the cut-away portion of the partition plate contacts with andpasses through the sensor positioned in the cut-away portion. Therefore,the sensor effectively detects a state (oxygen concentration, etc.) ofthe exhaust gas discharged from the respective discharge ports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 explains a catalyst integrated exhaust manifold of a firstembodiment to which an exhaust manifold according to the presentinvention is adapted, in which (a) is a sectional view of the catalystintegrated exhaust manifold, and (b) is a perspective view of apartition plate.

FIG. 2 is a sectional view taken along the line A-A of FIG. 1(a).

FIG. 3 explains a catalyst integrated exhaust manifold of a secondembodiment to which an exhaust manifold according to the presentinvention is adapted, in which (a) is a sectional view of the catalystintegrated exhaust manifold, and (b) is a perspective view of apartition plate.

FIG. 4 explains a catalyst integrated exhaust manifold of a thirdembodiment to which an exhaust manifold according to the presentinvention is adapted, in which (a) is a sectional view of the catalystintegrated exhaust manifold, and (b) is a perspective view of apartition plate.

FIG. 5 explains a flow rate analysis for exhaust gas using an exhaustmanifold according to the present invention, in which (a) is a partlyexploded perspective view of the exhaust manifold used in theexperiment, (b) is a transverse section of an exhaust collecting portionexplaining gas passage area, and (c) shows flow rate distribution at acenter of the catalyst for exhaust gas respectively discharged from thedischarge ports.

FIG. 6 is a sectional view of a conventional catalyst integrated exhaustmanifold, in which an exhaust manifold is joined to a catalyst containerfor accommodating a catalyst with a tilt angle.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

With reference to the attached drawings, a first embodiment of thepresent invention will be described below.

Firstly, a catalyst integrated exhaust manifold according to the firstembodiment, to which an exhaust manifold of the present invention isadapted, will be described with reference to FIGS. 1 and 2.

The exhaust manifold according to this embodiment relates to an exhaustsystem of an inline four-cylinder engine.

As shown in FIG. 1(a), a catalyst integrated exhaust manifold 1 includesa catalyst container 3 in which a catalyst 2 is accommodated, and anexhaust manifold 4 joined to the catalyst container 3 with a tilt angle.

The catalyst 2 converts detrimental component contained in exhaust gasthat is discharged from each discharge port E1, E2, E3, E4 of the engineinto harmless component. The catalyst 2 carries a three-way catalyst forcleaning CO, HC and NO_(x) on a surface of a one-piece cast carrierhaving a large number of gas flow passages in the form of a honeycombcross section and consisting of ceramic or heat resistant steel foil.

The catalyst container 3 is for accommodating the catalyst 2 and isjoined to the exhaust manifold 4 with a tilt angle.

The exhaust manifold 4 includes a plurality of branch pipes 6 a, 6 b, 6c and 6 d communicating with corresponding discharge ports E1, E2, E3and E4 of the engine via a discharge port flange 5, an exhaustcollecting portion 7 where the plurality of branch pipes 6 a, 6 b, 6 cand 6 d are collected, and a partition plate 8 dividing the interior ofthe exhaust collecting portion 7.

The illustrated four-cylinder engine is formed such that when thecylinders are referred to as a first cylinder, a second cylinder, athird cylinder, and a fourth cylinder in the order from the left side ofFIG. 1(a), ignition is made in order of the first cylinder, the thirdcylinder, the fourth cylinder, the second cylinder, and the firstcylinder.

As shown in FIG. 2, the exhaust collecting portion 7 is divided by thepartition plate 8 into two chambers, that is, a first chamber 7A and asecond chamber 7B. The branch pipes 6 a and 6 d communicate with thefirst chamber 7A and the other branch pipes 6 b and 6 c communicate withthe second chamber 7B.

The partition plate 8 is cut away to provide a cut 9 at one side of theend surface portion 8A located toward the catalyst 2. The first chamber7A and the second chamber 7B are communicated to each other through thecut 9.

Reference numeral 10 indicates an O₂ sensor for detecting oxygenconcentration in exhaust gas and carrying out a feed back control of theair/fuel ratio. ECU (not shown) controls, based on the detection valueof the O₂ sensor, to increase the amount of fuel injection when theair/fuel ratio becomes lean (excessive amount of O₂) and to decrease theamount of fuel injection when the air/fuel ratio becomes rich (lack ofoxygen).

The probe portion of the O₂ sensor 10 positions at the cut portion ofthe partition plate 8 so that the oxygen concentration of the exhaustgas that is discharged from each discharge port can be detectedeffectively.

Because the feed back control of the air/fuel ratio is carried out withthe use of a single O₂ sensor in the illustrated example, the cylindercurrently combusting is discriminated, for example, with a crank anglesensor (not shown) and a cam angle sensor (not shown), and anappropriate control is performed for increasing or decreasing the amountof fuel injection relative to a particular cylinder. Discrimination ofthe cylinder is not limited to the above example using a crank anglesensor and a cam angle sensor, and any other known methods can be used.

Operation of the catalyst integrated exhaust manifold 1 constructed asabove will be described with consideration of a flow of exhaust gas.

According to the engine of this embodiment, ignition is made in order ofthe first cylinder, the third cylinder, the fourth cylinder, the secondcylinder, and the first cylinder. For this reason, combustion gas withinthe combustion chamber is discharged in order from the first dischargeport E1, the third discharge port E3, the fourth discharge port E4, thesecond discharge port E2, and the first discharge port E1. The exhaustgas flow discharged from the first discharge port E1 flows down thebranch pipe 6 a of the exhaust manifold 4, and through the first chamber7A of the exhaust collecting portion 7 it flows into the catalyst 2.Next, the exhaust gas flow discharged from the third discharge port E3flows down the branch pipe 6 c of the exhaust manifold 4, and throughthe second chamber 7B of the exhaust collecting portion 7 it flows intothe catalyst 2. The exhaust gas flow discharged from the fourthdischarge port E4 flows down the branch pipe 6 d of the exhaust manifold4, and through the first chamber 7A of the exhaust collecting portion 7it flows into the catalyst 2. Further, the exhaust gas flow dischargedfrom the second discharge port E2 flows down the branch pipe 6 b of theexhaust manifold 4, and through the second chamber 7B of the exhaustcollecting portion 7 it flows into the catalyst 2.

In this instance, part of the exhaust gas flows that flow from thebranch pipes 6 a, 6 d into the catalyst 2 through the first chamber 7Aare flowed to the second chamber 7B through the cut 9 of the partitionplate 8 and then into the catalyst 2. Similarly, part of the exhaust gasflows that flow from the branch pipes 6 b, 6 c into the catalyst 2through the second chamber 7B are flowed to the first chamber 7A throughthe cut 9 of the partition plate 8 and then into the catalyst 2.

As described above, according to the catalyst integrated exhaustmanifold of this embodiment, providing a cut 9 at one side of the endsurface portion 8A of the partition plate 8 located toward the catalyst2 allows part of the exhaust gas flowing into the chambers 7A, 7B thatare divided by the partition plate 8 to flow into the opposite chamber7B, 7A through the cut 8 and then toward the catalyst 2. Therefore, evenin the case where the exhaust manifold 4 is joined to the catalystcontainer 3 with a tilt angle, it is possible to alleviate aconcentration of the flow of exhaust gas that flows from each chamber7A, 7B into the catalyst 2 only at a certain region of the large numberof gas flow passages of the catalyst 2, thereby preventing deteriorationof the catalyst 2 and retention of exhaust gas due to biased flow ofexhaust gas.

Further, because the O₂ sensor 10 is positioned in the cut-away portionof the partition plate 8, it is not necessary to provide an O₂ sensor 10for each chamber 7A, 7B, thereby decreasing the manufacturing cost ofthe catalyst integrated exhaust manifold 1.

The amount of exhaust gas that flows to the opposite chamber 7A, 7Bthrough the cut 9 of the partition plate 8 increases in proportion tothe opening area of the cut 9. Meanwhile, increasing the opening area ofthe cut 9 may cause an interference of the exhaust gases that flowthrough the cut 9 from the discharge ports E1, E2, E3, E4 of which orderof exhaust processes is continuous.

For this reason, it is preferable to set a proper opening area of thecut 9, for example, by taking into consideration of the mount angle ofthe exhaust manifold 4 relative to the catalyst container 3, that is,the angle of the exhaust gas flowing from the exhaust collecting portion7 to the catalyst 2.

Next, a second embodiment of the present invention will be describedwith reference to FIG. 3. Parts similar to those previously describedwith reference to the first embodiment are denoted by the same referencenumerals, and detailed description thereof will be omitted.

As shown in the figure, a catalyst integrated exhaust manifold 11according to this embodiment has substantially the same construction asthe catalyst integrated exhaust manifold 1 according to the firstembodiment. However, the partition plate 8 is cut away to provide cuts 9at both sides of the end surface portion 8A of the partition plate 8.

According to this catalyst integrated exhaust manifold 11, because thepartition plate 8 is provided with cuts 9 at both sides of the endsurface portion 8A, it is possible to more uniformly distribute a biasedflow of exhaust gas toward the catalyst 2.

The amount of exhaust gas that flows to the opposite chamber through thecuts 9, 9 increases in proportion to the total opening area of thesecuts 9, 9. Meanwhile, increasing the total opening area of these cuts 9,9 may cause an interference of the exhaust gases that flow through thecuts 9, 9 from the discharge ports E1, E2, E3, E4 of which order ofexhaust processes is continuous.

For this reason, it is preferable to set proper opening areas of thesetwo cuts 9, 9, for example, by taking into consideration of the mountangle of the exhaust manifold 4 relative to the catalyst container 3,that is, the angle of the exhaust gas flowing from the exhaustcollecting portion 7 to the catalyst 2.

Next, a third embodiment of the present invention will be described withreference to FIG. 4. Parts similar to those previously described withreference to the first embodiment are denoted by the same referencenumerals, and detailed description thereof will be omitted.

As shown in the figure, a catalyst integrated exhaust manifold 21according to this embodiment has substantially the same construction asthe catalyst integrated exhaust manifold 1 according to the firstembodiment. However, the partition plate 8 is provided with a cut 9 atthe opposite side of the O₂ sensor 10, and a clearance 12 is formedbetween the end surface portion 8A of the partition plate 8 that islocated toward the catalyst 2 and the upper surface of the catalyst 2.

Further, a recess 13 is provided at a position corresponding to theprobe portion of the O₂ sensor 10. The probe portion of the O₂ sensor 10is in the shape of a cylinder which is in conformity with the recess 13of the partition plate 8.

According to this catalyst integrated exhaust manifold 21, because ofthe cut 9 provided at one side of the partition plate 8 and theclearance 12 formed between the end surface portion 8A of the partitionplate 8 and the upper end of the catalyst 2, it is possible to moreuniformly distribute a biased flow of exhaust gas toward the catalyst 2.

The amount of exhaust gas that flows to the opposite chamber through thecut 9 and the clearance 12 increases in proportion to the opening areaof the cut 9 and the clearance 12. Meanwhile, increasing the opening areof these cut 9 and clearance 12 may cause an interference of the exhaustgases that flow through the cut 9 and the clearance 12 from thedischarge ports E1, E2, E3, E4 of which order of exhaust processes iscontinuous.

For this reason, it is preferable to set proper opening areas of thesecut 9 and clearance 12, for example, by taking into consideration of themount angle of the exhaust manifold 4 relative to the catalyst container3, that is, the angle of the exhaust gas flowing from the exhaustcollecting portion 7 to the catalyst 2.

Analysis Experiment

With the use of an exhaust manifold according to the present invention,experiment was made for analyzing how the exhaust gas discharged fromeach discharge port flows to the catalyst.

FIG. 5 explains a flow rate analysis for exhaust gas using an exhaustmanifold according to the present invention, in which (a) is a partlyexploded perspective view of the exhaust manifold used in theexperiment, (b) is a transverse section of an exhaust collecting portionexplaining gas passage area, and (c) shows flow rate distribution at acenter of the catalyst for the exhaust gas respectively discharged fromthe discharge ports.

The analysis experiment was carried out with the use of an inlinefour-cylinder engine and with the engine speed kept at 3000 rpm. Theanalysis experiment was carried out to measure the flow rate of exhaustgas at a center part (line A-A) of the catalyst 2 at a time when exhaustgas flows out from each discharge port E1, E2, E3, E4.

The catalyst integrated exhaust manifold shown in the figure isconstructed such that the partition plate 8 is provided with a cut 9 atone side of the end surface portion located toward the catalyst, and anO₂ sensor 10 is positioned in the cut 9 portion. A clearance (not shown)is also formed between the end surface portion of the partition plate 8and the upper surface of the catalyst 2.

Herein, the area of the cut 9 is set to be 18% of one gas passage areaPA or the other gas passage area PA at the lower end of the exhaustcollecting portion 7 (one half of the area that is obtained by excludingthe transverse cross-sectional area of the end surface portion of thepartition plate 8 from the transverse cross-sectional area of the lowerend of the exhaust collecting portion 7). When the cross-sectional areaof the O₂ sensor 10 is included, the opening area of the cut portionbecomes 15% of the gas passage area.

With reference to FIG. 5(c), it can be understood that part of theexhaust gas discharged from each discharge port E1, E2, E3, E4 flows tothe opposite chamber through the cut 9 and thereafter flows into thecatalyst 2.

Therefore, it is possible to distribute part of the exhaust gas thatflows through each chamber to the opposite chamber, so as to preventdeterioration of the catalyst 2 and retention of exhaust gas due tobiased flow of exhaust gas.

While the present invention has been described in detail with referenceto specific embodiments thereof, it will be apparent to one skilled inthe art that various changes and modifications may be made withoutdeparting from the scope of the claims.

For example, the above-described catalyst integrated exhaust manifolds1, 11, 21 have been described as of a 4-2-1 exhaust system for use in afour-cylinder engine. However, it may be adapted to a 6-2-1 exhaustsystem for use in a six-cylinder engine.

Further, it may be possible to arbitrarily change the position, thenumber, the opening area of cuts 9 provided in the partition plate 8and/or the area of the clearance 12 formed between the end surfaceportion 8A of the partition plate 8 located toward the catalyst 2 andthe upper end of the catalyst 2, etc. For example, a cut 9 may beprovided at a center of the partition plate 8 or at a center of the endsurface portion 8A.

1. An exhaust manifold which is joined to a catalyst container foraccommodating a catalyst with a tilt angle, comprising: a plurality ofbranch pipes communicating with corresponding discharge ports of anengine; an exhaust collecting portion where the plurality of branchpipes are collected; and a partition plate dividing an interior of theexhaust collecting portion, wherein the partition plate is cut away atan end surface portion located toward the catalyst.
 2. An exhaustmanifold according to claim 1, wherein a sensor is provided at thecut-away portion of the partition plate.